Method for producing cellulose shaped-bodies

ABSTRACT

Process for manufacture of cellulose mouldings, such as fibres, filaments, or films, from TCF-bleached or ECF-bleached cellulose, in which the bleached cellulose is dissolved in an aqueous tertiary aminoxide to form a mouldable cellulose, the cellulose solution deforms, and the moulding comes into being by coagulation of the deformed solution, characterized in that, to reduce the cellulose decomposition in the process, TCF-bleached cellulose is used comprising carboxyl group content in the range from 1 to 35 μmol/g or an ECF-bleached cellulose with carboxyl group content in the range from 1 to 50 μmol/g. Cellulose mouldings having a reduced cellulose decomposition may be formed by said process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is filed under the provisions of 35 U.S.C. §371 andclaims the priority of International Patent Application No.PCT/DE00/03408 filed Sep. 29, 2000, which in turn claims priority ofGerman Patent Application No. 199 48 401.5 filed Oct. 7, 1999.

FIELD OF THE INVENTION

The invention relates to a process for the manufacture of cellulosemouldings, such as fibres, filaments, or films, from TCF-bleached orECF-bleached cellulose, in which the bleached cellulose is dissolved inan aqueous tertiary aminoxide to form a mouldable cellulose solution,the cellulose solution deforms, and the moulding comes into being bycoagulation of the deformed solution. The invention also relates to theuse of a TCF or ECF-bleached cellulose pulp for the manufacture ofcellulose mouldings.

BACKGROUND OF THE INVENTION

The problems of the viscous process led to the development of newprocesses for the manufacture of regenerated cellulose mouldings, inwhich the cellulose is brought into solution without chemicalmodification. The fibres and filaments obtained from these solutions aregrouped under the designation “Lyocell”. Especially well-suited organicsolvents are tertiary aminoxides, in particularN-methylmorpholin-N-oxide (NMMO). A process for the formation of acellulose solution in aqueous NMMO is known from DE-A 44 41 468. Themanufacture of cellulose mouldings from these solutions is described inEP-A 0 574 870.

In this solution the dissolved cellulose and the solvents, under thethermal conditions of a chemical decomposition, leads to discolourationsof the spinning solution. Despite intensive washing of the cellulosemouldings formed, colouring substances remain in the mouldings, as aresult of which the degree of whiteness is impaired. In order to reducethe decomposition referred to, a stabilizer is therefore added to thespinning solution. Suitable stabilizers are known from EP-A 0 047 929and DD 218 104.

The principle is known from WO 97/23666 that the use of TCF-bleachedcellulose pulp in the Lyocell process leads to mouldings with a higherdegree of whiteness than the use of an ECF-bleached cellulose pulp. Bothcellulose pulps are manufactured with similar high initial degrees ofwhiteness of about 90% and high degrees of purity, in particular withregard to the lignin content. It therefore seems questionable whetherthe TCF-cellulose pulp in general produces better degrees of whitenessof the cellulose mouldings manufactured from this cellulose pulp than anECF-cellulose pulp.

DESCRIPTION OF THE INVENTION

The objective on which the present invention is based is the creation ofa process for the manufacture of cellulose mouldings with low cellulosedecomposition, based on TCF or ECF-bleached cellulose pulp. Thereduction in the cellulose decomposition is intended to be attainedessentially without special measures in the lyocell process. Additionaladvantages of the invention are derived from the following description.

The degrees of whiteness of cellulose pulp and fibre of a number ofdifferent cellulose pulp provenances were determined, which were eitherECF or TCF-bleached. The determination of the degree of whiteness of thecellulose pulp was carried out in accordance with DIN 53145, Part 2. Thedetermination of the degree of whiteness of the fibres was effected inaccordance with the method described in WO 97/23666, page 6. The averagedegree of polymerisation of the cellulose pulps according to the Cuoxammethod amounted to about 550 The degrees of whiteness measured at thefibre are compiled in Table 1.

TABLE 1 Initial degree Degree of of whiteness whiteness Degree ofwhiteness/ Manufacturing in cellulose of the cellulose pulp qualityprocess pulp spun fibre Cellunler F ECF 89.9 55.0 Messrs. Rayonier USA(Elementary Chloride-Free) Temfilm Example 1 TCF 87.5 55.3 Messrs.Tembec Canada (Total Chloride-Free) ALICELL ECF 88.2 58.6 Messrs.Western Pulp USA MoDo TCF 93.7 58.4 MoDo Paper Temfilm TCF 89.2 58.6Messrs. Tembec Canada

It can be seen from Table 1 that with ECE and TCE-bleached cellulosepulps of different provenances the degree of whiteness lies in a narrowrange between 87.5 and 93.7. The degree of whiteness. The degrees ofwhiteness of the spun fibres is likewise in a close range, between 55.0and 58.6. A higher degree of whiteness of the fibres spun fromTCF-bleached cellulose pulp was not perceptible.

Our researches have now revealed that the cellulose decomposition in thecourse of the Lyocell process, i.e. essentially from the formationthrough to the coagulation of the spinning solution, depends on thecarboxyl group content of the bleached cellulose pulp used to form thespinning solution. In this situation it has been shown that thecellulose decomposition of the spun fibres is less, the lower thecarboxyl group content is of the cellulose pulp used to form thesolution. It is therefore possible, according to the Lyocell process, tocreate cellulose fibres with reduced cellulose decomposition by makinguse of a TCF or ECF-bleached cellulose pulp with low carboxyl groupcontent for the formation of the spinning solution.

The objective referred to above is therefore resolved with the processreferred to in the preamble in that, in order to reduce the cellulosedecomposition in the process, a TCF-bleached cellulose pulp is used witha carboxyl group content in the range from 1 to 35 μmol/g or anECF-bleached cellulose pulp with a carboxyl group content in the rangefrom 1 to 50 μmol/g. It has also been shown that the cellulosedecomposition is the more restrained in the course of manufacture andprocessing of the extrusion solution, the lower the carboxyl groupcontent is of the cellulose pulp used. In order to achieve lowdecomposition of the cellulose and the aminoxide in the Lyocell process,TCF and ECF-bleached cellulose pulps are used in the manufacture of thespinning solution of which the carboxyl group content lies within therange indicated. Cellulose pulps with the carboxyl group contentsreferred to can be manufactured by a number of different cellulose pulpmanufacturers. As a result of the reduced decomposition of the spinningsolution components, fewer coloured constituents are also derived, withthe result that, as a secondary effect, the degree of whiteness of themoulding formed is also improved.

For preference a TCF-bleached cellulose pulp is used in the dissolvingstage with a carboxyl group content in the range from 15 to 30 μmol/g oran ECF-bleached cellulose pulp with a carboxyl group content in therange from 25 to 35 μmol/g. The determination of the carboxyl groupcontent of the celluloses which are to be used can be effected accordingto Döring; see K. Goetze, Chemical Fibres according to the ViscousProcess, Vol. 2, 1997 Edition, p. 1079.

The tertiary aminoxide used as the solvent in the preferred process ofthe invention is N-methylmorpholin-N-oxide-monohydrate (NMMO—MH).

In a further embodiment of the invention, a cellulose solution with acontent of alkalis or organic compounds can be formed, whereby thelatter contain at least four carbon atoms, at least two conjugateddouble bonds, and at least two substitutes —X—H, whereby X has thesignificance of O or NR, and R can be hydrogen or an alkyl group with 1to 4 carbon atoms. By means of these solution additives, the lowdecomposition achieved according to the invention can be reduced stillfurther. The quantity of the organic compound can lie in the range from0.01 to 0.5% by weight, related to the quantity of the solvent. Suitableorganic compounds are known from EP-A-0 047 929. A frequently usedcompound is isopropyl gallate.

By means of the process according to the invention, the decomposition ofthe cellulose is restricted to a fraction in the range from 3 to 20% byweight related to the cellulose pulp used. For preference the decomposedcellulose fraction lies in the range from 8 to 1.5% by weight.

The invention further relates to the use of a TCF-bleached cellulosepulp or an ECF-bleached cellulose pulp with a carboxyl group content inthe range from 1 to 35 μmol/g or 1 to 50 μmol/g respectively for theformation of a cellulose solution in a solvent containing tertiaryaminoxide for the manufacture of mouldings according to the Lyocellprocess. By means of the use of these cellulose pulps, not only is thedecomposition in the course of the Lyocell process reduced, but thedegree of whiteness of the mouldings formed is increased.

The invention is now explained in greater detail by the followingexamples.

EXAMPLES 1 to 6

Long-fibre sulphite cellulose pulp was bleached by alkalineperoxide-reinforced oxygen extracts, then bleached in a known mannerwith ozone and with peroxide. The bleaching methods are described, forexample, in R. P. Singh, The Bleaching of Pulp, TAPPI Press, Atlanta,USA. In this situation, three different carboxyl group contents are used(Examples 1 to 5). Three further samples of the cellulose pulp werebleached with hypochlorite. The degree of polymerisation and the initialdegree of whiteness of the pulps were determined in accordance with themethods referred to above, as were the carboxyl group and carbonyl groupcontents of the cellulose pulp. From the bleached cellulose pulps,spinning solutions with 13% cellulose, 10.5% water and 76.5% NMMO aremanufactured in a known manner. The solutions were spun in accordancewith the dry-wet process at 95° C. with a nozzle of 65 μm hole diameter.The degree of polymerisation and the degree of whiteness of the fibresobtained were determined. The determination of the degree ofpolymerisation was effected in accordance with the Cuoxam method. Thevalues obtained are indicated in Table 2.

TABLE 2 Example 1 2 3 4 5 6 Bleaching TCF TCF TCF ECF ECF ECF Carboxylgroup content 20.2 24.9 34.8 31.1 35.1 41.2 μmol/g Carboxyl groupcontent*) 52.1 48.2 35.6 26.1 24.5 82.2 μmol/g DP cellulose pulp 540 547560 555 566 550 DO fibre 519 505 470 485 465 440 DP decomposition % 3.97.7 16.1 12.6 16.8 20.0 Initial degree of 93.2 93.6 93.7 93.4 93.1 93.0whiteness of cellulose pulp Degree of whiteness 68.9 65.4 58.4 62.8 58.556.7 of fibre *)For determination see K. Goetze, op. cit.

It can be seen from Table 2 that, as the carboxyl group content of theTCF-bleached cellulose pulp and of the ECF-bleached cellulose pulpincreases, a substantial drop is to be observed in the degree ofpolymerisation and of the degree of whiteness of the fibre cellulose.For a given bleached cellulose pulp, the adjustment of the carboxylgroup content accordingly opens up the possibility of improving thetextile-physical properties of the spun fibre by way of the degree ofpolymerisation. Due to the reduced colour body formation in the courseof the process, a slow discolouration of the spinning bath sets in, as aresult of which costs advantages are derived in the regeneration of thesolvent media.

EXAMPLES 7 to 10

The degree of polymerisation, the carboxyl group content, the carbonylgroup content, and the initial degree of whiteness were determined fromfour bleached dissolving cellulose pulps. From the cellulose pulps, fourspinning solutions were manufactured with 13% cellulose, 10.5% water,and 76.5% NMMO. The zero shear viscosity of the spinning masses at 85°C. was measured (Haake RS 75, year of manufacture 1998). The spinningsolutions were spun at 95° C. with a nozzle of 65 μm hole diameter inaccordance with the usual dry-wet process. The degree of polymerisationof the celluloses was determined in the spinning solution, and thedegree of whiteness of the fibres. The results are compiled in Table 3.

TABLE 3 Example 7 8 9 10 Provenance/ Tembec MoDo Tembec Rayonierparameters Temfilm Paper TemSpr Cellunler Bleaching TCF TCF ECF ECF Zeroshear viscosity 6967 4588 4730 4720 DP cellulose pulp 538 510 520 510 DPspinning solution 490 455 452 450 DP decomposition [%] 9.9 10.8 13.111.7 Carboxyl group 20.9 24.4 36.8 28.8 content [μmol/g] Carbonyl group51.3 48.2 24.6 24.3 content [μmol/g] Initial degree of 90.5 92.1 91.192.1 whiteness Degree of whiteness 62.3 61.2 58.3 58.0 of fibre

The values from Table 3 also show that, as the carboxyl group contentincreases of the cellulose pulp used, the decomposition of the celluloseincreases and the degree of whiteness of the fibre deteriorates inrelation to the initial degree of whiteness.

1. A process for manufacture of cellulose mouldings with reducedcellulose decomposition from Total Chloride-Free (TCF) bleached orElementary Chloride-Free (ECF) bleached cellulose, comprising:dissolving a bleached cellulose pulp having a reduced number of carboxylgroups in an aqueous tertiary aminoxide to form a bleached cellulosesolution, wherein the reduced number of carboxyl groups causes reduceddecomposition of the bleached cellulose in the process, and wherein thebleached cellulose is selected from the group consisting of:TCF-bleached cellulose comprising a carboxyl group content in the rangefrom 1 to 35 mmol/g and ECF-bleached cellulose comprising a carboxylgroup content in the range from 1 to 50 mmol/g; deforming the cellulosesolution; and coagulating the deformed solution to generate a spinningsolution for forming the cellulose moulding.
 2. The process according toclaim 1, wherein the TCF-bleached cellulose comprises a carboxyl groupcontent in the range from 15 to 30 umol/g.
 3. The process according toclaim 1, wherein the ECF-bleached cellulose comprises a carboxyl groupcontent in the range from 25 to 35 umol/g.
 4. The process according toclaim 1, wherein of N-methylmorpholin-N-oxide is used as the tertiaryaminoxide.
 5. The process according to claim 1, further comprisingintroducing into the bleached cellulose solution at least one organiccompound comprising at least four carbon atoms, at least two conjugateddouble bonds, and at least two substitutes —X—H, whereby X has thesignificance of O or NR, and R is hydrogen or an alkyl group with 1 to 4carbon atoms.
 6. The process according to claim 5, wherein the organiccompound is isopropyl gallate.
 7. The process according to claim 1wherein the decomposition of the cellulose is restricted to a fractionin the range from 3 to 20% by weight, related to the cellulose pulpused.
 8. The process according to claim 1, wherein the cellulosemouldings include a member selected from the group consisting of:fibres, filaments, and films.
 9. The process according to claim 1,wherein the cellulose mouldings formed from the bleached cellulose pulphaving a lower content of carboxyl groups has a higher degree ofwhiteness relative to cellulose pulp having a higher content of carboxylgroups.
 10. The process according to claim 1, wherein the decompositionof the cellulose is restricted to a fraction in the range from 8 to 15%by weight, related to the cellulose pulp used.
 11. The process accordingto claim 1, wherein the cellulose solution comprises about 13%cellulose, about 10.5% water and about 76.5% of NMMO.
 12. The processaccording to claim 1, wherein the cellulose mouldings formed from thebleached cellulose pulp having a lower content of carboxyl groups has ahigher degree of polymerization relative to bleached cellulose pulphaving a higher content of carboxyl groups.
 13. The process according toclaim 1, wherein the bleached cellulose pulp having a lower content ofcarboxyl groups has a lower degree of decomposition relative to bleachedcellulose pulp having a higher content of carboxyl groups.
 14. Acellulose solution for the manufacture of mouldings comprising aTCF-bleach cellulose having a carboxyl group content in the range from 1to 35 μmol/g dissolved in a solvent containing a tertiary aminoxide. 15.A cellulose moulding article formed from a TCF-bleached celluloseaccording to claim
 14. 16. A cellulose solution for the manufacture ofmouldings comprising a ECF-bleached cellulose having a carboxyl groupcontent in the range of 1 to 50 μmol/g dissolved in a solvent containinga tertiary aminoxide.
 17. A cellulose moulding article formed from aTCF-bleached cellulose according to claim 16.